Environmental control apparatus of the type generally referred to as a heat pump has been known and utilized for some time. In general, such units include a condensor and an evaporator, connected in the system as a normal cooling system would be oriented. However, the heat pump generally comprises a reversing valve, connected to change the output connection from the compressor discharge line, so that it can supply either the indoor coil or the outdoor coil. This changes the operation or function of those coils between the condensor and evaporator function, and thus is able to change the system from a heating to a cooling system, and vice versa. As the cost of energy has risen very rapidly in recent years, heat pumps have been employed more frequently and considerable attention has been given to upgrading the control of such systems.
A significant advance in the area of heat pump controls is described and claimed in the application entitled "Heat Pump Control System", in the name of Frank Eugene Wills, which was filed Oct. 15, 1976, received Ser. No. 732,674, now U.S. Pat. No. 4,102,389, and is assigned to the assignee of this application. In that system, most of the controls were located in a single logic module, physically positioned in the heat pump installation where the electromechanical units of the heat pump are positioned. That is, the heat pump actuators such as the defrost relay, the compressor relay (sometimes termed a compressor contactor), and the electric heat sequencers are the electro mechanical units regulated by the output signals from the logic module. Even with this salutory advance in the heat pump art, there are still mechanical and/or electrical malfunctions of equipment which require diagnosis by a trained service technician. In addition it frequently happens that a thermostat may be improperly installed, or the interconnecting wiring between the thermostat and the logic module is improperly installed. For these reasons, it is desirable to have a diagnostic system which readily and accurately detects any system malfunctions, whether in the equipment installation or in subsequent wear of the system.
It is therefore a primary object of the present invention to provide a diagnostic system for use with the heat pump control system, which can effect all the diagnostic operations from a single location.
A more particular object of the present invention is to provide such a diagnostic system which not only analyzes the thermostat, module and heat pump components, but also draws power for its own operation from the system under test.